In message , The Medway Handyman
writes
Could you elaborate on that please Dave? I recently bought a 'bargain'
Bosch 9.6v driver and the charger seems very basic. Bosch tech
services confirm that the charger only has a 'power' light & doesn't
switch off when the battery is fully charged, and that the re charge
time is 3-5 hours which has to be timed manually.

Those are the worst type of charger since it's easy to forget the
battery is on charge and the charge current is above the level where it
can be left on charge indefinitely.

Even the most basic chargers like the Ryobi one hour type use a thermal
switch in the pack to detect the end of charge when the batteries
suddenly start getting warm. Proper charge detection uses negative
delta V which monitors for a sudden voltage fall at the end of charge
due to bubbles on the electrode surface.

A perfect battery that actually used a pressure switch internally to
detect the pressure build up at the end of charge was developed by
Uniross (I think). You simply couldn't overcharge those cells, but they
were expensive and weren't promoted properly.

I've looked at buying a spare battery, but that exceeds the cost of the
driver and isn't viable. I love the little Bosch machine for suitable
jobs, but I'm completely confused about the charging thing.

If you can handle a super long recharge time you could hack the charger
by adding a higher value of series resistor to lower the current to
something suitable for unattended charging.

--
Clive Mitchell
http://www.bigclive.com